We demonstrate a way of controlling planar defect modes in three-dimensional photonic crystals. Modification of the profile of the interfaces between the photonic crystals and the defect changes the boundary condition of the defect modes. This change brings about modulation of the frequency of the defect modes. A planar defect in three-dimensional photonic crystals has two interfaces between the defect and photonic crystals. They can support surface modes. When the frequency of a planar defect mode comes into the surface modes, the defect mode is assisted by the surface mode. If the frequency comes near the band edge, the defect mode couples to a standing wave at the band edge. Otherwise, the planar defect modes are not excited so effectively because reflection from photonic crystals is diffraction.